Neuroinflammation is integral to numerous central nervous system (CNS) pathologies including infectious, neurodegenerative and demyelinating autoimmune diseases typified by multiple sclerosis (MS). In MS and its mouse model, experimental autoimmune encephalomyelitis (EAE), inflammation is caused by microglia (MG), resident macrophages (M?) of the brain parenchyma, and bone marrow (BM)-borne M? that infiltrate CNS as the blood-brain barrier deteriorates. Although historically linked to antigen presentation, MG and M? are emerging as independent drivers of disease; they phagocytose myelin, release inflammatory cytokines (TNF, IFN?) and mediators of cell injury, and perpetuate tissue damage. The relative contribution of MG vs. M? to MS pathogenesis and the underlying transcriptional networks remain controversial. There is no cure for MS however, glucocorticoids (GC) and IFN ? are first-line agents to manage relapses. GC receptor (GR) is a transcription factor that can directly bind palindromic GC response elements and activate associated genes or `tether' to DNA-bound NFkB and AP1 and broadly repress their inflammatory targets, e.g., Tnf, Il1a, Il1 b, Il12b. In both contexts, GR utilizes a unique cofactor, the GR-interacting protein (GRIP)1, whose conditional loss in M? derepresses dozens of inflammatory genes sensitizing mice to acute and chronic inflammation. The protective role of IFN? in MS is less understood, and type I `IFN signature' is a hallmark of autoimmunity. IFN signaling occurs in two waves whereby activation of IFN regulatory factors (IRF)3/7 and the Infb gene is followed by IFN? activating the Stat1/Stat2/IRF9 heterotrimer and IFN-stimulated genes (ISG). Notably, we identified M? GRIP1 as an IRF 3/7/9 coactivator, required for full induction of Ifnb and other ISG. As GC and IFN? pathways are both therapeutic in MS/EAE and rely on GRIP1, we predicted GRIP1 loss to aggravate disease. In stark contrast, myeloid cell-specific GRIP1 KO ameliorated EAE, including passive EAE when WT myelin-reactive T-cells were adoptively transferred to WT or KO recipients, thus implicating GRIP1 in the MG/M?-driven effector stage of the disease. Intriguingly, despite milder symptoms, KO mice were fully resistant to IFN? therapy. Our objective in this R21 project is to explore the unexpected role of GRIP1 in neuroinflammation. We hypothesize that GRIP1 performs two distinct functions in MS/EAE: it supports the effector stage of EAE pathogenesis, yet, mediates therapeutic actions of IFN?, possibly, by acting in different CNS myeloid cell subsets. Our Specific Aims are to: 1) Assess, in parabiosis and BM chimera studies, the relative contribution of GRIP1 in MG vs. M? to EAE pathogenesis and efficacy of IFN? therapy; 2) Identify, through RNAseq, ATACseq and single-cell RNAseq, GRIP1-dependent epigenomic and transcriptional pathways in MG and M? that regulate CNS inflammation. The successful completion of this project will reveal the role of a multifaceted cofactor GRIP1 in MG- and M?-specific transcriptional networks of MS pathogenesis and treatment with additional implications for the functions of GRIP1 in other inflammatory CNS pathologies.